Why are they attacking Republican voters?

Historically, rule number one of politics is don't attack the voters. When Romney said he wouldn't represent half the country, it cost him the election. [link to www.salon.com (secure)]

While Romney said it to a small group in what he thought was a private moment, it still cost him the election. Since 2016 the media and some Democrats are now vilifying Republican voters. It begs the question, why does this seem like a good idea to them, it only further drives away voters from the rust belt. It is therefore not meant to win over Republican voters; but, that isn't the purpose.

The Democrats have a very divided party. The attacks on the conservatives are meant to unify the Democratic base and quell the progressives within their own party against the big bad orange man and his supporters. I would love to hear others thoughts on this strange political tactic.